The disclosure of Japanese Patent Application No. HEI 11-197403 filed on Jul. 12, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a valve driving apparatus and a valve driving method for an internal combustion engine in which each cylinder is provided with a plurality of exhaust valves that are electromagnetically opened and closed.
2. Description of the Related Art
To improve the fuel economy and emission quality of internal combustion engines, exhaust gas recirculation (hereinafter, referred to as xe2x80x9cEGRxe2x80x9d) systems for introducing exhaust gas into combustion chambers have been developed. Of the EGR systems, a generally-termed internal EGR system, in particular, controls the open-close timing of exhaust valves so that exhaust gas flows back into the combustion chambers during the intake stroke.
In an internal combustion engine equipped with electromagnetically driven exhaust valves, in particular, an appropriate amount of EGR can be achieved by adjusting the open-close timing of the. exhaust valves and the valve lift thereof in accordance with the operational condition of the engine, as described in Japanese Patent Application Laid-Open No. HEI 2-294547.
In some engines, each cylinder is provided with a plurality of electromagnetically driven exhaust valves. By simultaneously driving the exhaust valves of each cylinder of such an engine, the flow resistance can be reduced during the exhaust stroke so as to quickly discharge exhaust gas. However, if the required EGR amount is relatively small during the EGR control, it becomes necessary to open and close each exhaust valve in a very short time. Furthermore, if the required EGR is small, adjustment based on the valve lift becomes necessary.
To open an electromagnetically driven valve, a series of operations is performed based on the characteristics of the electromagnetically driven valve. That is, the valve body of the electromagnetically driven valve is released from a state in which the valve body is fixed at a closed valve position by controlling the electromagnetic force, and then the valve body is moved to and fixed at an open valve position by using electromagnetic force and a spring force. To close the electromagnetically driven valve, a series of operations for releasing the valve body from a state in which the valve body is fixed at the open valve position through control of the electromagnetic force and then moving the valve body to and fixing it in the closed valve position by using the electromagnetic force and the spring force is performed. Therefore, the valve opening timing is controlled based on a combination of the valve opening operation and the valve closing operation described above. Since a minimum operation time exists for each of the valve operations, the reduction of the EGR amount is also limited.
To achieve a reduced valve lift of an electromagnetically driven valve, a series of operations is performed. That is, the valve body of the electromagnetically driven valve is temporarily released from the state in which the valve body is fixed at the open valve position through control of the electromagnetic force, and then the valve body is moved back to and fixed at the closed valve position by the electromagnetic force. During the operation of temporarily releasing the valve body and then returning the valve body to the original position, the valve body temporarily undergoes a floating state. Therefore, the valve lift pattern is susceptible to environmental changes.
Therefore, in an engine in which a plurality of electromagnetically driven valves are provided for each cylinder, controllability of the EGR amount may degrade if the required EGR amount is relatively small.
Accordingly, it is an object of the invention to provide a valve driving apparatus and a valve driving method for an internal combustion engine having a plurality of electromagnetically driven valves for each cylinder that are capable of preventing degradation of the controllability of the EGR amount even if the EGR amount is small.
To achieve the aforementioned and other objects, a valve driving apparatus for an internal combustion engine in accordance with a first aspect of the invention includes a plurality of electromagnetically operated exhaust valves that are provided for each cylinder of the internal combustion engine, the plurality of exhaust valves including at least one first exhaust valve and at least one second exhaust valve. The valve driving apparatus comprises an exhaust valve driver which, in a first mode when exhaust gas recirculation is performed independently of an exhaust stroke, drives the at least one first exhaust valve and does not drive the at least second exhaust valve. In this valve driving apparatus, the exhaust valve driver performs the exhaust gas recirculation by driving only a limited number of the plurality of exhaust valves of each cylinder, instead of driving all the exhaust valves, when the exhaust gas recirculation is performed independently of the exhaust stroke. Therefore, the open valve duration of the exhaust valves for achieving the required ECR amount becomes longer than the corresponding open valve duration in the case where all the exhaust valves are driven. Furthermore, the incidence of a case where adjustment based on the amount of valve lift is needed is reduced.
Therefore, the degradation of the controllability of the EGR amount can be substantially prevented even if the required EGR amount is small.
In the first aspect of the invention, the valve driving apparatus may further include an exhaust gas recirculation amount calculator that determines a required exhaust gas recirculation amount in accordance with an operational condition of the internal combustion engine. During the exhaust gas recirculation performed independently of the exhaust stroke, the exhaust valve driver enters a first exhaust gas recirculation mode of performing the exhaust gas recirculation by driving only the limited number of the plurality of exhaust valve of each cylinder, when the required exhaust gas recirculation amount determined by the exhaust gas recirculation amount calculator is less than a recirculation amount criterion. When the required exhaust gas recirculation amount is greater than the recirculation amount criterion, the exhaust valve driver enters a second exhaust gas recirculation mode of performing the exhaust gas recirculation by driving all the plurality of exhaust valves of each cylinder.
That is, if the required EGR amount (required exhaust gas recirculation amount) determined by the exhaust gas recirculation amount calculator is less than the recirculation amount criterion in the exhaust gas recirculation performed independently of the exhaust stroke, the exhaust valve driver enters the first exhaust gas recirculation mode, that is, performs the exhaust gas recirculation by driving only the limited number of exhaust valve of each cylinder. Therefore, the open valve duration of the exhaust valves for achieving the required EGR amount becomes relatively long, and the incidence of adjustment based on the amount of valve lift becomes relatively low. Hence, the degradation of the controllability can be substantially prevented even if the required EGR amount is small.
When the required exhaust gas recirculation amount is greater than the recirculation amount criterion, the exhaust valve driver may enter the second exhaust gas recirculation mode, that is, perform the exhaust gas recirculation by driving all the exhaust valves of each cylinder. Thus, the exhaust gas recirculation is performed by driving all the exhaust valves if, despite driving all the exhaust valves, the open valve duration of the exhaust valves does not become so short as to degrade the controllability. Therefore, even if the required EGR amount is considerably great, the exhaust gas recirculation can be reliably and appropriately performed.